The present invention relates to a laser system for transferring energy to tissue during medical treatment procedures and, more particularly, to a system and method of measuring and controlling temperature of an optical fiber tip for the laser treatment system during operation.
It is well known that energy generators in the form of lasers have been utilized to treat many disease states, including cancer, tumors, and benign prostatic hyperplasia (BPH). During the course of such treatments, one parameter which has great importance is the temperature of the tissue being treated. For example, the current recommendation for forming lesions in the prostate as a treatment for BPH is to heat a small volume of tissue to 85° C. for approximately three minutes. It will be appreciated that heating the tissue at a lesser temperature has the effect of incomplete lesion formation, while heating the tissue at a higher temperature can cause excessive tissue damage. Accordingly, the ability to accurately measure the temperature of the optical fiber tip during treatment, as well as control the power output of the laser to maintain the temperature at a desired level, is of primary concern.
It will be understood that there are several known ways of performing the temperature monitoring function for a laser system. One approach has been utilized in a laser treatment system known as the “Indigo 830e Laseroptic Treatment System” manufactured by Ethicon EndoSurgery, Inc. of Cincinnati, Ohio, which is also the assignee of the present invention. This approach involves relying upon the temperature dependence of the fluorescent response of a slug of material at the fiber tip to an optical stimulus. More specifically, a pulse of pump energy causes a fluorescence pulse in an alexandrite slug which is delayed by a time interval corresponding to a temperature of the material. By providing the stimulus signal in the form of a sinusoid, the response signal is likewise a sinusoid and the temperature is related to the phase shift or difference therebetween.
The signals which are compared in the 830e laser treatment system are the actual response or fluorescent signal from the alexandrite and a pair of timing signals (shifted 0° and 90° in phase) which are programmed in its electronics. In this way, digital timing signals are used to strip phase information from the response signal. It has been found, however, that several adjustments and calibrations are required under this approach due to the chain of amplifiers and filters involved. This not only adds complexity and cost to the set-up and maintenance of such systems, but creates an inherent variability between each laser treatment system that must be accommodated during manufacture and service.
Accordingly, it would be desirable for a system and method to be developed in which temperature of an optical fiber tip used with a laser device during treatment is able to be measured and controlled in a manner which minimizes the adjustments and calibrations required, improves the stability and repeatability between laser systems, and reduces complexity and cost.